Process for making cylindrical bodies

ABSTRACT

A manufacturing aid for layered plastic containers comprises pressure elements suitable to apply a pressure to a strip of heated plastic material so as to improve its adhesion to a surface toward which said pressure is applied.

FIELD OF THE INVENTION

The present invention relates to cylindrical bodies made by extruding layers of plastic material on a revolving cylindrical form. More particularly, the invention relates to a manufacturing aid that permits to perform the process with high efficiency and improved quality and accuracy.

BACKGROUND OF THE INVENTION

Cylindrical tanks are used for the storage of liquids and other materials, e.g., particulate solids. The tanks are used for the storage of many different materials and therefore need to be suitable for different conditions, such as temperature, density and weight. The suitability of the tank to its intended use is a function of the diameter, height and thickness of the tank. The size of the tank is determined by cylindrical form used as an extrusion surface, and the thickness of the tank is determined by the extrusion die that determines the strip dimensions, and the number of layers that determine the thickness of the tank.

An example of this method is U.S. Pat. No. 6,102,241 which discloses the extrusion process. Although this method allows manufacturing cylinder tanks by extrusion, the placement of the strips on the cylindrical form has some disadvantages. Since there is a distance between the die and the cylindrical form, the strips leave the die, continue to move through air until they reach the form. Those conditions cause an undesirable deformation of the strips, which is more significant as the rotation speed decreases and the strips are suspended in the air and under the pull of gravity for a longer period of time. The tension in the strips is also subject to changes as a result, and it needs to be adjusted to an optimal value, influencing many important parameters such as the thickness of every strip, the amount of material used to form the tank, the cooling rate etc. Another disadvantage of prior art methods is the fact that there is no way to prevent the movement of the strips after they leave the die and this, therefore, causes a lack of accuracy in the placement of the strips on the cylinder, which can cause undesirable spaces or overlapping strips and waste of material.

To date the prior art has failed to provide means for accurately placing the strips on the form during the manufacturing process. It is an object of the present invention to provide a device that significantly improves the placement process of the extruded strips and thus the quality of the final product.

Other objectives and advantages of the invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

The manufacturing aid for layered plastic containers according to the invention comprises pressure elements suitable to apply a pressure to a strip of heated plastic material so as to improve its adhesion to a surface toward which said pressure is applied. The pressure elements can be, e.g., rollers the position of which is changeable so as to position at least two rollers in a desired positioned relationship with the surface to which pressure is applied.

According to one embodiment of the invention the surface is the surface of a cylindrical form.

According to another embodiment of the invention each of the rollers is held in a fixed position by two supporting rods connected to a supporting frame. In this embodiment of the invention the rods can be positioned at different locations on the frame, and each roller can be positioned at different locations along its supporting rods. Preferably, but not limitatively, the length of each roller is at least approximately equal to the width of the strip.

The invention is also directed to a method for improving the layering of a plastic cylindrical body, comprising applying to the extruded strip that is layered on a form, a manufacturing aid according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a side view of the manufacturing aid structure according to one embodiment of the invention;

FIG. 2 is a perspective view of the manufacturing aid structure of FIG. 1;

FIG. 3 is a top view of the manufacturing aid structure of FIG. 1; and.

FIG. 4 is a bottom view of the manufacturing aid structure of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention allows the manufacturing of tanks that are used for the storage of different materials, in an improved process, by using a manufacturing aid structure, resulting in higher efficiency and improved quality and accuracy than can be currently achieved by prior art systems.

The manufacturing of the tank is performed by extruding strips 102 that are made of extruded plastic material, on a cylindrical form 101. The plastic material is heated, passed through the die of an extruder, and shaped as strips. Strips 102 are wound on the cylindrical form 101 surface while it is revolving around its axis and at the same time, the extrusion die moves in a direction essentially parallel to the ground and away from the form, as illustrated by arrow B in FIG. 2, which that relative motion is achieved between form and die. Of course, in principle, the die may be stationary and the form may move, although in most cases this will be less convenient.

With reference to FIG. 1 through 4, the manufacturing aid comprises at least two rollers 103 that are held in a fixed position, each by two supporting rods 104 connected to a supporting frame 105. The rollers 103 are suitable to apply a pressure to a strip 102 so as to improve its adhesion to the surface of the cylindrical form 101, toward which the pressure is applied. The position of the rollers 103 can be changed so as to position them in a desired positioned relationship with the surface of the cylindrical form 101, by placing the rollers 103 at different locations along the rods 104. The rods can also be placed in a desirable positioned relationship with the frame 105, e.g., by changing the height of their location. The fact that the position of the rollers 103 can be changed is important in order to finely tune the manufacturing aid to the size of the cylindrical form 101.

Any suitable pressure element can be used, as long as it applies a uniform pressure across the strip. For instance, a ball-shaped pressure element can be used, if the diameter of the ball is large enough. Of course, different pressure can be applied for different purposes, or different products or even at different times in the same manufacturing cycle.

The strip 102 emerges from the die and continues its movement toward the cylindrical form 101 on rollers 103. This method prevents the deformation of the strip 102 that can be caused by the pull of gravity when there is no support for it. Another advantage of this device and method is the fact that the rollers 103 keep the strip 102 on a straight path until it reaches the cylindrical form 101, and by that allows an accurate placement of strip 102 thereon. To perform this process, the length of each roller needs to be at least approximately equal to the width of strip 102.

All above description has been provided for the purpose of illustration and is not intended to limit the invention in any way, except as defined by the claims to follow. 

1. A manufacturing aid for layered plastic containers, comprising pressure elements suitable to apply a pressure to a strip of heated plastic material so as to improve its adhesion to a surface toward which said pressure is applied.
 2. A manufacturing aid according to claim 1, wherein the pressure elements comprise a roller.
 3. A manufacturing aid according to claim 2, comprising at least two rollers
 4. A manufacturing aid according to claim 3, wherein the rollers' position is changeable so as to position said at least two rollers in a desired positioned relationship with the surface to which pressure is applied.
 5. A manufacturing aid according to claim 1, wherein said surface is the surface of a cylindrical form.
 6. A manufacturing aid according to claim 3, wherein each of the said at least two rollers is held in a fixed position by two supporting rods connected to a supporting frame.
 7. A manufacturing aid according to claim 6, wherein said rods are positioned at different locations in said frame.
 8. A manufacturing aid according to claim 6, wherein a roller is positioned at different locations along its supporting rods.
 9. A manufacturing aid according to claim 2, wherein the length of each roller is at least equal to the width of the strip.
 10. A method for improving the layering of a plastic cylindrical body, comprising applying to the extruded strip that is layered on a form, a manufacturing aid according to claim
 1. 